It is generally known that unless there is considerable activity, such as boating, swimming, water skiing and the like, on a particular small body of water, the water will stagnate and become cloudy. Additionally, it is recognized that this type of water would have a low level of dissolved oxygen which is known as a major source of fish kills in water used to raise various aquatic animals, such as catfish. If the circulation of the water is not maintained by natural or artificial means, the water would have a tendency to "stratify", manifested by different levels of dissolved oxygen and different water temperatures at different depths. This stratification can have a disastrous effect on the health and condition of the developing fish.
Two basic forms of aerators and destratifiers have been utilized to prevent the development of stratification in these ponds. These aerators and destratifiers operate by either spraying jets of water into the air or by agitating the water by use of one or more mechanical paddle wheels or similar agitators.
Mechanical paddle wheel devices in common use today all employ external flotation devices, paddle wheels attached to external drive shafts, and drive motors mounted on a frame that exposes them to water and atmospheric conditions. The motor, frame and flotation devices are stationary and drive the paddle wheel by use of this external shaft which rotates in bearings.
Many problems in manufacturability and reliability are inherent in these designs. Obviously, exposure of the motor demands either an expensive weather-proof motor or a weather shield or housing surrounding the motor. The shaft and bearings must also be designed so as to resist the deleterious effects of the weather. Furthermore, they must also be carefully maintained and periodically lubricated because of their direct exposure to the water. These components will constantly collect algae and water-born deposits that will also require periodic cleaning and maintenance. Surmounting these inherent problems adds considerably to the costs of manufacturing and operating these agitators and destratifiers.
U.S. Pat. No. 3,322,410 issued to Ahlenius, U.S. Pat. No. 3,911,065 issued to Martin et. al., U.S. Pat. No. 4,409,107 issued to Busch and U.S. Pat. No. 4,681,711 issued to Eaton are typical of these prior art water agitator devices. For example, the patent to Busch describes a method and apparatus for aerating bodies of water utilizing a rotating paddle wheel having a plurality of paddles mounted on a shaft. The paddle wheel is powered by a motor which is provided under an arch-like motor cover to shelter it from rain and other adverse elements. The patent to Ahlenius illustrates a water purification unit for use on small bodies of water to remove surface algae and the like. The unit contains a paddle wheel provided within a box. A motor is provided on the top wall of the box and drives the paddle wheel by means of a chain affixed to a sprocket connected to the motor drive shaft and a second sprocket affixed to the axle of the paddle wheel. Both the patents to Martin et. al. and Eaton describe liquid aerators provided with an uncovered motor.